Machines make glass bottles by placing a portion of molten glass, or a "gob" of glass, into a mold and pressing and/or blowing air or other gas into the center of the gob. This causes the hot glass to expand to the side of the mold and take on the shape of the mold. Before the glass is introduced into and formed in the mold, the raw glass must first be heated in a furnace normally located above the mold. The hot glass gob is conditioned (or cooled slightly) in a fore-hearth to a temperature consistent with a glass viscosity suitable for the forming operation. The glass is then dropped down through the fore-hearth and into the mold for forming, e.g., blowing. The fore-hearth extrudes hot molten glass that is cut into substantially uniformly weighted, but non- spherically shaped glass gobs produced intermittently.
The glass gobs drop from the fore-hearth into a guide funnel, which keeps the gobs oriented and may shape them to properly engage a gob scoop and the mold. The gobs typically fall a distance ranging from about 6 to 24 inches (15.24 to 60.96 cm). The gobs have a tendency to tip as they fall and it is beneficial to have a funnel means of correcting their attitude before entering a gob scoop and placement into a blank mold. After passing through the funnel and the gob scoop, the gobs are typically directed to placement into one of a plurality of molds by means of troughs. After placement into a mold, the gobs are blown or otherwise formed into a product shape.
The funnel must withstand an extreme environment. The interior must contact intermittent molten glass gobs that can range in temperature up to about 2300.degree. F. (1260.degree. C.) for typical glass compositions, up to about 2732.degree. F. (1500.degree. C.) or more for high silica content glasses. Typically, the (softening) temperature of the glass gobs ranges from about 2000.degree. to 2200.degree. F. (1093.degree. to 1204.degree. C.), but may be as low as about 1500.degree. F. (816.degree. C.).
Glass gobs are typically cylindrical in form and sheared from a flow of molten glass as it exits from the fore-hearth, the glass gobs having weights ranging from about 1/4 to 31/2 pounds (0.113 to 1.59 kg), but more typically in the range from about 1/2 to 11/2 pounds (0.227 to 0.680 kg). The gob's representative diameter can range from about 3/4 to 2 inches (1.91 to 5.08 cm). The number of gobs passing through a given funnel typically ranges from 80-150 per minute or 4800-9000 per hour. These frequencies and extreme gob temperatures, sizes, weights, and dropping energies of the gobs are interspersed with exposure to ambient air temperatures ranging up to about 200.degree. F. (93.3.degree. C.), typically about 150.degree. F. (65.6.degree. C.) because of the proximity of the furnace.
The kinetic energy of the gobs being dropped, when combined with the intermittent high temperature shock of the gobs, tends to damage the interior of almost any funnel. Materials that can withstand continuous exposure to the glass gob temperatures tend to be brittle and subject to cracking when exposed to thermal and structural shock. Even if cracking or other failures are avoided, cooling of the funnel at the exterior surface (or at internal cooling passages) is needed to maintain the structural integrity of many funnel materials of construction at these high temperature conditions. Presently, metallic funnels must be cooled well below the temperatures of the glass gobs. This is typically accomplished by circulating large volumes of water in external jackets.
Some recently developed funnels are composed of carbon fitted for forced air cooling instead of water. The carbon funnels have been machined with a plurality of baffles or fins to achieve sufficient cooling using forced air. The baffles or fins protrude into the forced air stream at least about 1/8 inch (0.318 cm).
However, these funnels erode in this harsh environment. Typically, the erosion is not equally distributed around the circumference of the funnel, but tends to be in one angular location. The angular location of maximum erosion is primarily a function of funnel location and orientation with respect to the fore-hearth. These location specific failure modes have resulted in a shortened useful life and costly replacement of funnels.
It would be advantageous to have a funnel that did not need to be replaced as frequently and that did not need to be cooled by fluids driven by mechanical means and/or require the complicated machined cooling passage/baffle/fin shapes required by forced air cooling.